Anti-theft system designed using IR LED, TSOP IR sensor, NE555 and LM311
An alarm which rings when someone crosses a door is a simple anti-theft system designed using infra red. Here, we will design a simple circuit to make such an anti-theft system. Circuit is done as shown in the following diagram. Circuit will have two parts. A transmitter circuit and a sensor circuit. In the transmitter circuit, VR indicates variable resistor.
Working of circuit
Transmitter circuit have an IR LED which always emit infra red rays. These rays are pointed to the TSOP IR sensor connected to the sensor circuit as shown in the circuit. If TSOP IR sensor is receiving IR rays, buzzer in the sensor circuit will not make sound. If TSOP sensor is not receiving infra red rays, buzzer will make sound.
Application of circuit
IR transmitter and receiver are arranged in such a way that TSOP sensor will always receive IR rays from the transmitter circuit. When someone crosses these rays, TSOP sensor will not receive IR rays and buzzer will make sound. That is, if the system is activated, when someone crosses these rays, that will be a thief and buzzer will make sound.
Watch the video demonstration here.